Membrane filter plate

ABSTRACT

Membrane filter plate for a filter press or the like, with a carrier plate, at least one membrane arranged on one side of the carrier plate and preferably provided with spacing cams or the like for applying a filter cloth or the like and a sealing edge surrounding the carrier plate and membrane and interconnecting them in a substantially flow medium-tight manner, the peripheral surface or surfaces of said sealing edge parallel to the carrier plate median plane being arranged in the unloaded normal position thereof on the side having the membrane or on either side of the carrier plate, while being spaced from the membrane plane, wherein the contact surface of the carrier plate facing the membrane runs towards the carrier plate median plane in a transition area located between the connecting line of the membrane with the sealing edge and the central area of the carrier plate, in which it extends parallel to said central plate median plane.

This application is a divisional application of Ser. No. 07/330,310filed Mar. 29, 1989, now U.S. Pat. No. 4,897,190 which was a divisionalapplication of Ser. No. 07/246,914, filed Sept. 16, 1988, which issuedas U.S. Pat. No. 4,832,840 on May 23, 1989, and was a continuationapplication of Ser. No. 07/036,133, filed Apr. 6, 1987 (now abandoned),which was a continuation of application Ser. No. 06/673,206filed Nov.19, 1984 (now abandoned), which was a continuation of application Ser.No. 06/450,786, filed Dec. 17, 1982 (now abandoned).

The invention relates to a membrane filter plate for a filter press orthe like, with a carrier plate, at least one membrane arranged on oneside of the carrier plate and preferably provided with spacing cams orthe like for applying a filter cloth or the like and a sealing edgesurrounding the carrier plate and membrane and interconnecting them in asubstantially medium-tight manner, with respect to flow the peripheralsurface or surfaces of said sealing edge parallel to the carrier platemedian plane being arranged in the unloaded normal position thereof onthe side having the membrane or on either side of the carrier plate,while being spaced from the membrane plane.

A difficulty of the hitherto used filter membrane plates is thatmechanical stressing of the membrane under the varying compressionstresses of the aforementioned type is extremely high, so that themembrane can easily fracture in the vicinity of the connecting line withthe sealing edge. This disadvantage has been even more serious in that,therefore, in the hitherto largely used one-piece construction of themembrane with the sealing edge and carrier plate, it has not beenpossible to optimise the material characteristics of the membraneindependently of the requirements of high bending strength orflexibility, etc., to be made on the carrier plate and sealing edge.

The problem of the invention is to provide a membrane filter plate ofthe aforementioned type, whose membrane has a significantly improvedservice life compared with those used hitherto. Preferably, it shouldalso be possible to optimize the material characteristics of theindividual components of the membrane filter plate, particularly theactual membrane, with a view to the intended use.

According to the invention, this problem is solved in that the contactsurface of the carrier plate facing the membrane extends towards thecarrier plate median plane in a transition area located between theconnecting line of the membrane with the sealing edge and the centralarea of the carrier plate, in which it extends parallel to said carrierplate median plane.

According to the invention, the contact surface of the carrier platefacing the membrane, for producing in each case one predeterminedbending line for the filtration or squeezing phase, from the connectingline of the membrane with the sealing edge is initially constructedsubstantially parallel to the carrier plate median plane, then slopestowards it and then extends parallel to the carrier plate median planeover the substantially the entire central area of the carrier plate.

According to a special embodiment of the invention, the peripheralsurface of the sealing edge parallel to the carrier plate median planein the direction of the center of the membrane filter plate is linkedwith an interface sloping towards the carrier plate median plane andwhich drops with a step to the connecting line of the membrane with thesealing edge.

In addition, the slope of the interface to the carrier plate medianplane can be greater than that of the chamfered area of the contactsurface.

According to the invention, the height of the step can optionally besubstantially the same as that of the spacing cams or spacers.

According to another embodiment of the invention, in the transitionarea, whilst avoiding clearly defined bendng lines, the contact surfaceis constructed as a bevel surface passing into the central area of thecarrier plate and with a continuously changing curvature from theconnecting point into the carrier plate surface. This embodiment has thespecial advantage that in the transition area between the sealing edgeand the central area, the material stresses of the membrane are keptparticularly small.

As a result of the bevel surface with continuously varying curvature,optionally whilst leaving a planar central area, it is possible in thetransition area between the central area of the membrane filter plateand the sealing edge to reduce the material stressing of the membrane,on passing from the normal position into the pressing or filtrationposition to such an extent that the membrane material can beadvantageously optimized towards the remaining requirements,particularly e.g. the chemical resistance to the medium to be filtered.As a result of the shape of the transition area of the carrier plate, asignificantly reduced surface tension of the membrane in the variousoperating states is acheived, so that there is a considerably improvedresistance to chemical stressing (stress corrosion). Due to the bevelsurface provided, it is possible to use much thicker membranes than whenthere is a single or multiple hinge in the bending area of the membrane,so that the life of the membrane and its stressability are furtherincreased.

To ensure the possibility of higher temperatures of use of the membranefilter plate according to the invention, it is also proposed to providea contact area between the carrier plate and the membrane which isreduced as compared with an areal contact. In addition, it is alsoproposed that the contact surface of the carrier plate or the membranesurface facing the carrier plate is provided with. As will be describedhereinafter, membrane filter plates constructed in this way can be usedin advantageous manner for filtering very hot and also very cold media.

In particular, between the cooling or heating medium ducts can be formedand cooling or heating media can flow through the membrane chamberdefined by the contact surface and the membrane. Furthermore, themembrane chamber can be subject to the action of the same flow medium,with a pressure controllable as a function of the operating phase, inboth the filtration phase and in the pressing phase.

It is in particular also proposed that the supporting surfaces of thecarrier plate spacers facing the membrane are chamfered in the vicinityof the bevel surface in accordance with their general configuration.

If, in the manner described hereinabove, the contact surface of thecarrier plate has a system of spacing cams, the resulting reduction inthe area of contact between carrier plate and membrane leads to athermal separating layer between them, which prevents the carrier platefrom being subject to the action of the medium to be filtered, which maybe at a relatively high temperature and which acts on the membrane, innormal operation during the filtration phase. This carrier plate coolingaction is naturally also aided if, according to the invention, thespacing cams form a system of coolant ducts through which flows acoolant, e.g. compressed air, also in the filtration phase.

The resulting thermal decoupling of the carrier plate from the membranemeans that even at high temperatures of e.g. 90° C., hitherto consideredtoo high for plastic membrane filter plates, there is neither aninadmissible material stressing, nor a warping of the carrier plate.Such warping action always occurs if the carrier plate is zonallysubject to the action of the high temperature of the medium to befiltered, because as a result of its zonally differing thickness, theplate will then become heated and expand to varying extents. Carrierplate warping of this type, which naturally leads to correspondingwarping of the complete membrane filter plate, cause differentthicknesses of the press cake produced in the pressing phase and thismay lead to problems in any following washing process. The inventioneliminates all these problems in that, although the membrane is subjectto relatively high temperature of the medium to be filtered, whichgenerally has a favourable influence on its flexibility, the carrierplate is only exposed to a much lower temperature. If desired, thecoolant flow can be made so high that the membrane is also cooled, sothat it is not thermally overstressed in the case of very hightemperatures of the medium to be filtered. It has proved advantageous touse membrane filter plates of the aforementioned type in such a way thatin succession a membrane filter plate and a conventional chamber filterplate, i.e., without membrane are provided, which permits an optimumutilization of the outwardly directed curvature of the individualmembrane in the pressing phase. In the case of media which have veryhigh temperatures and which have to be filtered, it is obvious that onlymembrane filter plates according to the invention should be combined ina filter press, in order in this way to ensure cooling of all theplates.

However, in connection with membrane filter plates, problems not onlyoccur when they are used at high temperatures of e.g. 90° C. and it isin fact also difficult to treat media to be filtered having particularlylow temperatures, especially below ambient temperature and especiallybelow 0° C. This can once again lead to warping of the carrier plate, ifthis is subject to the action of the low temperature of the medium to befiltered. However, in particular the membrane itself largely loses itselasticity, so that in the case of the membrane movement necessary inthe pressing phase, there are severe membrane material stresses,particularly at the fixing point, so that fatigue failures and otherdamage can occur. However, the membrane filter plate of theaforementioned type can be used very satisfactorily when the media to befiltered are at low temperatures, by using a heating medium instead of acoolant. This in particular makes it possible to process media which areto be filtered cold, which were hitherto considered unfilterable withplastic membrane filter plates of the aforementioned type.

The reason for this is that the heating medium flowing through theheating medium ducts not only prevents a cooling of the carrier plate tothe lower temperature of the medium to be filtered, which preventswarping and the like, but in particular while engaged with the carrierplate, the membrane is kept at a higher temperature than the medium tobe filtered, so that in the pressing phase the membrane has a muchhigher elasticity than would be the case at the temperature of themedium to be filtered. Thus, the membrane remains completely mobile anddamage thereto, particularly in the edge area, as can occur withstiffening of the membrane due to an excessively low temperature, isreliably avoided.

According to the invention, it is also possible for the sealing edge tobe formed by a sealing edge frame, at least on one side of the carrierplate median plane, whereby the membrane is sealingly received betweenthe frame and the carrier plate surface extending up to the edge area ofthe membrane filter plate extending at right angles to the carrier platemedian plane. In particular, the separating plane between the sealingedge frame and the carrier plate surface can be substantially in theplane of the membrane in its unloaded normal position in the edge areaof the carrier plate.

The invention also proposes that the sealing edge frame is at leastzonally welded to the carrier plate. In particular, the sealing edgeframe can be welded exclusively in the angle area of the angularlyconstructed carrier plate.

According to another embodiment of the invention, the sealing edge frameis at least zonally connected to the carrier plate by means of dowelspassing through bores extending at right angles to the carrier platemedian plane in the sealing edge frame or frames, the carrier plate andthe membrane or membranes. It is in particular proposed that the dowelsare held at least partly by force fit in the material surrounding them.

According to the invention, the membrane bore surrounding the dowel hasa larger diameter than the dowel and a ring seal is placed in the thusformed annulus surrounding the dowel.

The invention also proposes that the carrier plate, which has a membraneon either side, is joined to the two sealing frames by a retaining clipmade from plastic, metal, etc.

According to another embodiment of the invention, the retaining clip hasa web running at right angles to the carrier plate median plane and twoframe pins running inwards and parallel to the carrier plate medianplane and which engage in corresponding bores of the sealing edge frame.In particular, the retaining clip has a central, inwardly projectingplate pin, located substantially in the carrier plate median plane andwhich engages in a corresponding bore of the carrier plate edge.

The invention also proposes that at least part of the pin is held in thebores by force fit. The invention also provides that at least part ofthe pin is bonded in the bores with surrounding material. The inventionalso proposes that at least part of the pin is welded in the bores withthe surrounding material.

According to the invention, the plate pin is optionally constructedlonger than the frame pin. The retaining clip also has a locking pin forhanging up the filter cloth which projects outwards substantially intothe carrier plate median plane.

According to the invention, the locking pin can also be tapered close toits free end. According to a special embodiment, the locking pin isrounded close to its free end.

The invention proposes a membrane filter plate of the aforementionedtype, in which in the central area of the carrier plate there is atleast one preferably circular support, whose support surface parallel tothe carrier plate median plane is substantially aligned with theperipheral surface of the sealing edge parallel to said median plane,characterized in that the support has a base part projecting from thecarrier plate surface substantially up to the plane of the membrane inits unloaded normal position, said base part having an end faceextending parallel to the carrier plate median plane and an interfacesloping from the end face to the carrier plate surface, as well as asupport part substantially projecting from the plane of the membrane inthe unloaded normal position up to the support face, whereby an obliqueinterface runs in the direction of a membrane from the substantiallyplanar support face of the support part.

In particular, the interface of the base part and/or the interface ofthe support part can be offset in stepped manner at its end remote fromthe front or support face. According to the invention, the base part isconstructed in one piece with the carrier plate. The base part can alsobe placed on the carrier plate which is substantially planar in itscentral region.

According to another embodiment of the invention, the base part and/orsupport part can be welded to the carrier plate. The base part and/orsupport part can be dowelled to the carrier plate.

According to the invention, the dowel or dowels are at least partly heldby force fit in the material surrounding them. According to theinvention, the dowel or dowels can at least be partly welded into thematerial surrounding them. As an alternative, the invention proposesthat the dowel or dowels are at least partly bonded to the materialsurrounding them. In addition, the base part and/or support part can bescrewed to the carrier plate.

According to a special embodiment, the invention proposes a membranefilter plate of the aforementioned type, which is provided with acentral inlet and which is characterized in that in the sealing regionsurrounding the central inlet, the membrane is sealingly joined to thecarrier plate by means of an annular carrier bracket, whereby the endface remote from the carrier plate has a smaller distance from thecarrier plate surface than the interface or interfaces of the sealingedge parallel to the carrier plate plane.

In particular, it can be provided that the carrier bracket is rounded onits edge remote from the central inlet. The invention particularlyproposes that the central inlet is surrounded by a thrust ring, whoseinternal diameter is larger than the diameter of the central inlet andagainst which the membrane engages.

According to the invention, the support ring has a bevel surfaceextending substantially obliquely up to the carrier plate surface fromthe plane of the membrane, in its unloaded normal position, in thedirection of the central inlet, and that the carrier bracket isconstructed complementary to the bevel surface in the area correspondingthereto.

According to another embodiment of the invention, the carrier bracket iswelded to the membrane and/or the support ring and/or the carrier plate.The carrier bracket can also be bonded to the membrane and/or thesupport ring and/or the carrier plate.

According to the invention, the carrier bracket is screwed to themembrane and/or the support ring and/or the carrier plate. It is alsoproposed that the carrier plate is dowelled to the membrane and/or thesupport ring and/or the carrier plate. The dowel is at least partly heldby force fit in the material surrounding it. It is also proposed thatthe dowel is at least partly bonded to the material surrounding it. Theinvention also optionally proposes that the dowel is at least partlywelded to the material surrounding it. The invention also proposes thatthe carrier bracket is constructed in one piece with the membrane.

The invention also proposes a membrane filter plate, wherein the endface of the support ring facing the membrane, starting from its inneredge, for producing two predetermined bending lines for the membrane, itis initially substantially parallel to the carrier plate median plane,then slopes towards the latter and is then stepped towards the carrierplate surface.

The invention also proposes a membrane filter plate, wherein there is alocking ring passing through the central inlet for holding together thecarrier bracket or brackets and the carrier plate.

According to a preferred embodiment, the individual parts are made atleast partly from plastic. At least the membrane can be made from amaterial, which differs from that of the carrier plate and/or thesealing edge.

The invention also proposes that the membrane is made from aself-sealing material. The membrane can also be made from rubber or thelike.

According to a further embodiment of the invention in the case ofsubstantially rectangular construction of the sealing edge and carrierplate, the transition between the narrow sides of the membrane is ineach case formed by a quadrant. In addition, the invention also providesfor the distance of the membrane from the carrier plate surface beingapproximately 1/3 of the distance from the peripheral surface of thesealing edge parallel to the carrier plate median plane.

According to a further development of the invention, in its unloadednormal position, the membrane forms a substantially flat slab. Theinvention also proposes forming slots for constituting supply anddischarge channels in the sealing surface of the sealing edge framefacing the membrane.

A further development of the invention provides for the carrier plate tohave a substantially all-around weld overflow slot in its edge areaadjacent to the sealing edge frame.

Finally, the invention also proposes the interchangeability of themembrane, whereby the latter can in particular have arresting and/orcentering points or surfaces or the like, preferably in the vicinity ofthe sealing edge frame and/or the central inlet. In particular, thismakes it possible, for example, to easily carry out a filter cloth ormembrane change, because the joining together of the individual partscan be rapidly and reliably realized without the aid of an additionaladjusting means or the like.

It is pointed out that the term sloping or oblique in conjunction withthe configuration of the contact surface of the carrier plate towardsthe carrier plate median plane, or in conjunction with the interface ofthe base part and/or the support part, as well as in conjunction withthe bevel surface of the support ring and finally the end face of thesupport ring towards the carrier plate median plane, is understood toindicate an angle of 3° to 15° and preferably 5° to 10° .

The membrane filter plate proposed by the invention can be made from alarge number of suitable materials. Advantageously, for example, thecarrier plate can be made from polyproplene, which is also very suitablefor the sealing edge frame. Due to the necessary tolerance requirements,it is not generally possible to use materials which are difficult tomachine in those cases when it is only possible to obtain the necessarytolerances by mechanical refinishing. It is also possible to use rigidfoams, in addition to the thermoplastic materials normally used for suchcomponents.

If thermoplastic materials are used, the shaping process canadvantageously be employed for producing membrane filter plates of thetype according to the invention. The dowels used in several embodimentscan also be made from several materials, the function of the dowel beingon the one hand the cohesion and dimensional fixing of the individualparts and on the other to absorb certain forces. Thus, for example, theedge dowels extending substantially at right angles to the carrier platemedian plane have the function of transferring to the carrier plate, theinternal force (filtration pressure) acting on the chamber-side bevel ofthe sealing edge, if this force component cannot be compensated by thefrictional force in the sealing edge area, i.e. by the closing pressure,thereby preventing a bending out of the sealing edge. The necessarynumber and the dimensions of the dowels, as well as their distributionand materials, can be worked out by those skilled in the art on thebasis of the constructional requirements.

When using weldable membrane filter plates in which all components aremade from polypropylene or the like, it is advantageous for cost reasonsto optionally only provide a local welding, e.g. in the corner area ofthe membrane filter plates, preferably only in the vicinity of thecorner bores, for which purposes e.g. resistance welding (with copperwire inserts or the like) is suitable, as is h.f. welding.

If an interchangeable membrane is used, if the latter is not made from asealing material such as rubber, it is necessary to provide seals in thecorners, i.e. in the vicinity of the corner bores and said seals cannaturally also be arranged e.g. around the dowels, although this is notabsolutely necessary. The thickness of the seal naturally correspondsroughly to that of the membrane and has a plus tolerance dependent onthe Shore hardness.

It is again stressed that in the case where no welding is used, in whichthe individual parts are exclusively held together by the sealing edgedowels, etc, or by retaining clips, it is possible to freely choose thematerials for each individual part. The membranes are interchangeable.No complicated surface configuration in the sealing edge frame area isprovided, so that no tolerance problems can occur when changing themembrane and instead a completely satisfactory seal is always ensured.For example, when using thermoplastic materials, the sealing edge framecan be produced by known, proven welded structures. If the membrane isto be produced from a thermoplastic material, it can e.g. be made bystamping or shaping an extruded plate or by shaping from powder orgranular material in the compression mould. Rubber membranes can also bevulcanized without difficulty in the planar, uncomplicated formaccording to the invention. While taking account of this materialvariant, a mould can be constructed by means of which both plastic andrubber membranes can be produced in a single shape, which makes itpossible to considerably cut the manufacturing costs of the membranefilter plate according to the invention. Despite its simple shape, themembrane engages completely tightly between the sealing edge frames, asa result of the dimensions of said frames and the carrier plate. Anall-round edge support is formed between these parts on which themembrane completely engages and which ensures that the membrane has inthe hereinbefore and hereinafter described manner two separatehinge-like movement zones in the particular predetermined bending lines,one of which is provided for each movement direction.

ON THE DRAWINGS

The invention is described in greater detail hereinafter relative tonon-limitative embodiments and the attached drawings, on which

FIG. 1 is a plan view of a first embodiment of a membrane filter plateaccording to the invention in plan view.

FIG. 2 is a sectional view of the sealing edge of the membrane filterplate of FIG. 1 in section along line II--II of FIG. 1 in a larger-scalerepresentation.

FIG. 3 is a larger-scale representation of a corner area of the membranefilter plate of FIGS. 1 and 2 with details of the supply and dischargebores, partly in section.

FIG. 4 is a sectional view taken along line IV--IV of FIG. 3.

FIG. 5 is a sectional view taken along line V--V of FIG. 3.

FIG. 6 illustrates a modified embodiment of the construction of themembrane filter plate corner area in plan view.

FIG. 7 is a sectional view taken through a membrane filter plate similarto FIG. 4, the membrane movement being indicated.

FIG. 8A is a side view and FIG. 8B is an end view of a dowel usable inthe membrane filter plate according to the invention.

FIG. 9A is a side view and FIG. 9B is an end view of a retaining clipusable in a membrane filter plate according to the invention.

FIG. 10 is a sectional illustration of a support of an embodiment of theinvention in a section at right angles to the carrier plate medianplane.

FIG. 11 is a sectional view taken through a central inlet of anembodiment of the invention.

FIG. 12 is a sectional view taken through another embodiment of acentral inlet of a membrane filter plate according to the invention.

FIG. 13 in section at right angles to the plate plane of the areaadjacent to the sealing edge of a first embodiment of the membranefilter plate according to the invention in the filtration phase.

FIG. 14 is a representation corresponding to FIG. 13 of the sealing edgearea with the membrane in the unloaded state.

FIG. 15 is a view to FIG. 13 of the sealing edge area of a secondembodiment of a membrane filter plate according to the invention in thepressing phase.

FIG. 16 is a sectional view illustrating the sealing edge area shown inFIG. 15, but in the filtration phase.

FIG. 17 is a sectional view illustrating the sealing edge area of FIGS.15 and 16 in the unloaded membrane state.

FIG. 18 is a sectional view illustrating the sealing edge area of themembrane filter plate of FIGS. 14 to 17 when incorporated into a filterpress and with the membrane unloaded.

FIG. 19 is a sectional view illustrating the sealing edge area of FIG.18, but in the filtration phase.

FIG. 20 is a sectional view illustrating the sealing edge area of FIGS.18 and 19 in the pressing phase.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As can be seen in FIG. 1, the membrane filter plate shown in plan viewtherein has in its central area a substantially planar carrier platesurface 12, covered by a membrane 14 made from flexible material, suchas plastic, rubber, etc., which is not shown in FIG. 1, but which can beseen in FIG. 2 and which is sealingly held in the edge area 16 of themembrane filter plate. FIG. 1 also shows that there is a corner inlet 18and that the four narrow sides of membrane 14 are in each case connectedby quadrants to radius R. In the case of a membrane filter plate withthe conventional dimensions 1200×1200 mm, then the radius R is e.g. 320mm.

As can be gathered from the detail of FIG. 2, a membrane 14 is arrangedon either side of carrier plate 20, whose longitudinal median plane is22. To the right of FIG. 2, it is possible to see that membrane 14,provided on its side facing carrier plate surface 12 with spacing cams24, spacing ribs, etc., for the application of a filter cloth 26 shownto the left in FIG. 2, is sealingly received between the edge area 16 ofcarrier plate 20 and a sealing edge frame 28. In the fitted state ofFIG. 2, membrane 14 is in its unloaded, normal position in which itforms a substantially flat slab. In the embodiment shown to the right inFIG. 2, the sealing edge frame 28 is connected by means of a dowel 30 tothe edge area 16 of carrier plate 20, the dowel being received by forcefit in the bore which receives it. However, it can also be bonded orwelded, if the material from which membrane 14 is made permits this. Itwould naturally also be possible to provide a screwed connection betweenthe sealing edge frame 28 and carrier plate 20. The right-hand part ofFIG. 2 also shows that edge area 16 of carrier plate 20 has a weldoverflow slot 32, which serves to receive the weld overflow in the case,as shown in the left-hand part of FIG. 2, when sealing edge frame 28,membrane 14 and carrier plate 20 are welded together. However, animportant part is also played by the weld overflow slot 32 in theembodiment to the right in FIG. 2 in which there is no welding and inwhich the membrane which is tightly clamped between sealing edge frame28 and edge area 16 of carrier plate 20. Thus, slot 32 reduces thebearing surface between the spacing edge frame 28 and edge area 16 ofcarrier plate 20 and consequently increases the pressure on membrane 14in the actual sealing area surrounding dowel 30, so that the sealingaction is improved. The circumferential surface 34 of sealing edge frame28 parallel to the carrier plate median plane 22 and to which is appliedfilter cloth 26, firstly extends parallel to the carrier plate surface12 with a spacing such that on assembling a series of membrane filterplates of the indicated type in filter presses, the in each case desiredfilter chamber volume defined by in each case two membranes 14 or thefilter cloths applied thereto is obtained.

FIG. 2 also shows that the contact surface 36 of carrier plate 20 facingmembrane 14, starting from the connecting lines 38 of membrane 14 withsealing edge 34, the membrane 14 runs substantially parallel to thecarrier plate median plane 22, then slopes towards the latter and thenas a carrier plate surface 12 parallel to carrier plate median plane 22over substantially the entire central area of the carrier plate for thepurpose of producing two predetermined bending lines 40, 42, whosesignificance will be explained hereinafter relative to FIG. 7. FIG. 2also shows that the circumferential surface 34 of sealing edge frame 28parallel to the carrier plate median plane 22, close to the connectingline 38 between membrane 14 and frame 28 follows in the direction of thecenter of the membrane filter plate onto an interface 44 sloping in thedirection of the carrier plate median plane 22, said interface droppingwith a step 46 to the connecting line 38 of membrane 14 to sealing edgeframe 28. The slope of interface 44 towards the carrier plate medianplane 22 is greater than that of the chamfered area of contact surface36. The height of step 46 essentially corresponds to that of spacer 24,so that the filter cloth 26, in the position of membrane 14 to the leftof FIG. 2, which corresponds to the so-called filtration phase in whichthe membrane chamber 48 between membrane 14 and carrier plate surface 12is pressureless and consequently has a volume passing towards zero inthe manner shown to the left in FIG. 2, while the not shown filterchamber located to the left of filter cloth 26 in FIG. 2 is subject tothe action of pressurized medium to be filtered, passes from interface44 substantially parallel to contact surface 36 and without any steptowards the central area of the membrane filter plate. It is alsopointed out that the separating plane between the sealing edge frame 28and the edge area 16 of carrier plate 20 is naturally substantially inthe plane of membrane 14 in its unloaded normal position as shown inFIG. 2.

FIG. 3 shows the corner area of a membrane filter plate with supply anddischarge bores. It can be seen that a corner inlet 18 is connected viaa channel 50 with a series of transverse bores 52 which, as can be seenin FIG. 4, communicate with the particular filter chamber. In theembodiment shown to the left in FIG. 4, channel 50 is milled into thesurface of sealing edge frame 28 and the transverse bores 52 are opentowards the sealing surface of sealing edge frame 28 facing membrane 40.This permits particularly easy machining, because the lateral ends ofchannels 50 can be kept closed from the outset during the production ofthe sealing edge frame 28, so that there is no need for a subsequentfilling by welding or the like. However, the open channel constructionaccording to the left-hand part of FIG. 4 can only be used if thesealing edge frame 28 is not welded to carrier plate 20, becausenaturally the corresponding channels, bores or slots could otherwiseeasily become smeared.

However, channel 50 and transverse bores 52 are incorporated into thematerial of the sealing edge frame 28 in the embodiment shown to theright in FIG. 4, so that in this case easy welding is possible. Weldingis naturally impossible if membrane 14 is made from rubber or the like,so that the embodiment of the left-hand part of FIG. 4 is particularlysuitable when using a rubber, silicone rubber or similar membrane. Theembodiment to the right in FIG. 4 is recommended if a membrane made froma weldable material, e.g. polypropylene is used.

FIG. 5 shows a corner inlet 18 of the aforementioned type, in which theactual bore is surrounded by a ring seal 54 made from a sealingmaterial. This embodiment is recommended if membrane 14 is not made froma self-sealing material, e.g. if, like carrier plate 20 or sealing edgeframe 28, membrane 14 is made from a plastics material, likepolypropylene.

The detail of FIG. 6 shows that a corner bore 18, which does not serveas an inlet here, is closed by means of a dowel 30, followed by thecorner area 56, indicated by broken lines. The welding of one or morecorner areas 56 can take place e.g. by resistance welding (with aninserted copper wire or the like), whereby it is possible, if necessary,to use additional retaining elements, as will be explained in conjuctionwith FIG. 9, although the retaining devices shown therein can be usablewithout any welding of the individual membrane filter plate elements.

The embodiment of FIG. 7 shows that in the edge area 16 of carrier plate20 and/or in sealing edge frame 28, in each case on the outer edge face,bores 58, 60 are provided, which are used in conjunction with theretaining devices which will be described relative to FIG. 9. FIG. 7shows in particular the nature of the membrane movement obtainedaccording to the invention.

As can be gathered from the left-hand part of FIG. 7, in which membrane14 is shown in the position assumed during a filtration phase, in whichit tightly engages on carrier plate 20 with the membrane chamber volumepassing towards zero, membrane 14 engages in such a way on contactsurface 36 in the transition area between the sealing edge frame 28 andthe central region of carrier plate 20 that it is only curved around thepredetermined bending line 42, before gently passing into the centralregion of the membrane filter plate. However, to the right in FIG. 7, inthe so-called squeezing or pressing phase, membrane chamber 48 issubject to pressure action as a result of incorrect operation, i.e.without the medium to be filtered being supplied to the filter chamber,so that the rightward deflection of membrane 14 assumes a theoreticalmaximum. It can be seen that the bending down of membrane 14 takes placeexclusively around the predetermined bending line 40, whereas thepredetermined bending line 42 remains largely un-stressed. Due to theshaping of contact surface 36 according to the invention, a combinationof two "hinges" is obtained, which are formed by the predeterminedbending lines 40, 42, so that membrane 14 is protected fromoverstressing both in the case of correct operation according to theleft-hand part of FIG. 7, i.e. with a normal membrane lift, and in thecase of faulty operation, as shown to the right in FIG. 7.

FIGS. 8A, 8B shows a dowel 30 which, as shown, is conically taperedclose to its ends in order to facilitate driving into the bores 18 ofthe described type. Thus, in the fitted state, dowels 30 always extendat right angles to the carrier plate median plane 22 and serve either,in the case of welded joints, to close the bores 18 provided in thewelding area (like 56) or, corresponding to the force fit, which is e.g.used to secure the individual elements of the membrane filter platewithin bores 18 against forces acting parallel to the carrier platemedian plane, i.e. radial forces. In the case of a suitable connectionwith the surrounding material, e.g. by welding, bonding, powerful forcefit or screwing, dowels 30 can naturally also absorb forces acting atright angles to the carrier plate median plane 22.

For holding together the membrane filter plate elements against suchforces acting at right angles to the carrier plate median plane 22,retaining clip 60' of the type shown in FIG. 9A are used. Retainingclips 60' have a web and, at the side at the bottom in FIG. 9, two framepins 64 and a central plate pin 66. Frame pins 64 and/or plate pins 66are inserted in bores 58, 60 of the sealing edge frame 28 and/or edgearea 16 of carrier plate 20, connection once again taking place by forcefit, welding, etc, as described hereinbefore in conjunction with dowels30. On the side of web 62 opposite to plate pin 66 is provided a lockingpin 68, which is rounded at its free end and which is used for hangingup filter cloth 26. Around the membrane filter plate are providedseveral such retaining clips 60', so that not only is a reliable holdingtogether of the membrane filter plate elements against forces acting atright angles to the carrier plate median plane 22 ensured, but also thefilter cloths 26 can be adequately secured by means of the roundedlocking pins 68. Retaining clips 60' are preferably made from plastic,but other material, such as metal, can also be used. Preferably, and asshown in FIG. 9, web 62 is slightly angled in order to obtain aninternal tension of retaining clip 60', which aids the optionallydesired force fit of pins 64, 66 in bores 58, 60.

FIG. 10 shows two embodiments of the optionally provided support of themembrane filter plate according to the invention. Each of the supporthas a base part 70 extending from the carrier plate surface 12substantially to the plane of membrane 14 in its unloaded normalposition and which in the embodiment of the right-hand part of FIG. 10is constructed in one piece with carrier plate 20, whereas in theembodiment of the left-hand part of FIG. 10 is a separate member. Basepart 70 has an end face 72 extending parallel to the carrier platemedian plane 22 and an interface 74 sloping therefrom to the carrierplate surface 12. In addition, the support has a support part 78projecting substantially from the plane of membrane 14 in its unloadednormal position to a support face 76 from which an interface 80 slopestowards membrane 14. Both interface 74 of base part 70 and interface 80of support part 78 are offset in stepped manner in the vicinity of theirend face 72 or support face 76.

The base part 70 and/or support part 78 can be connected in various waysto the carrier plate 20, whilst incorporating membrane 14, e.g. screwed,welded or dowelled, as mentioned above with respect to the dowel 30. Inthe left-hand part of FIG. 10, it is also possible to see a centralscrew 82, which can optionally be screwed into an internal thread of thecorresponding bore of the carrier plate 20. However, it is naturallyalso possible to provide a bore passing through the complete arrangementat right angles to the carrier plate median plane 22 and into which isscrewed the screw 82, optionally using a not shown lock nut.

FIG. 11 and 12 show different embodiments of the central area of amembrane filter plate with a central filter inlet. In the sealing areasurrounding central inlet 84, membrane 14 is connected by means of anannular carrier bracket 86, whose different embodiments will beexplained hereinafter, to carrier plate 20 in sealing manner. The endface 88 of the different carrier brackets 86 remote from carrier plate20 has in each case a smaller distance from the carrier plate surface 12than the circumferential surface 34 of the sealing edge frame 28parallel to the carrier plate median plane 22.

In the left-hand embodiment of FIG. 11, the central inlet 84 is spacedlysurrounded by a thrust ring 90, (shown in phantom) whose internaldiameter is larger than the diameter of central inlet 84. In theembodiment of FIG. 11, the thrust ring 90 has a bevel surface 92extending from the plane of membrane 14, in its unloaded normal positionin the direction of the central inlet 84 and sloping up to the carrierplate surface 12. In this case, carrier bracket 86 is constructed in acompletely complementary manner to bevel surface 92 in the areacorresponding thereto, so that the membrane 14 is secured betweenbracket 86 and thrust ring 90.

In the embodiment on the right of FIG. 11, the carrier bracket 86 isrounded on its edge remote from the central inlet 84 and, without theinterposing of a thrust ring or the like, membrane 14 is directlyintroduced into the sealing gap between bracket 86 and carrier platesurface 12. The two carrier brackets 86 are fixed together in theembodiment of FIG. 11 by a screw 94, which either cooperates with acorresponding internal bore or a check nut or counter-bush. However, anoverall screwed system, as shown in FIG. 12 can also be used.

Carrier bracket 86 and/or thrust ring 90 can also be welded, bonded ordowelled to carrier plate 22 and/or the membrane, in the mannerdescribed hereinbefore. This also applies to the embodiment of thecentral inlet shown to the left in FIG. 12, in which the membrane 14 isconstructed in one piece with carrier bracket 86. A thrust ring is onceagain applied to carrier plate 20, said ring being constructed in thesame way as the aforementioned sealing edge frame 28 in such a way thatthe end face 96 of thrust ring 90 facing the membrane, as from the inneredge of the ring initially extends substantially parallel to the carrierplate median plane 22, then slopes towards the latter and is thenstepped towards the carrier plate surface 12, for producing twopredetermined bending lines 98, 100. This leads to the double hingeaction described in conjunction with the sealing edge frame 28 onpressurizing membrane 14.

In the embodiment on the right of FIG. 12, membrane 14 is constructed inone piece with the carrier bracket 86, but the latter is so thin thatthere is no risk of any bending stressing of membrane 14 andconsequently there is no need for a thrust ring. It is also possible tosee the locking ring (show in phantom) passing through central inlet forholding together carrier brackets 86 and carrier plate 20 and this cannaturally also be provided with the other embodiments of the centralinlet.

The individual parts of the aforementioned membrane filter plate can bemade at least partly from plastic in all the embodiments, it beingparticularly advantageous to optimize the material properties of eachindividual part, as a function of the particular requirements. Thus,particularly the membrane can be made from a self-sealing material, e.g.rubber and it is also interchangeable, so that this leads to furtherpossible uses of the membrane filter plate according to the invention.

In FIG. 14, the fitted membrane 14 is in its unloaded normal conditionand essentially forms a flat slab, whereas in FIG. 13, showing theso-called filtration phase, in which it is moved towards carrier plate20 by a pressurized medium to be filtered. In the embodiment of FIGS. 13and 14, the surfaces of carrier plate 20 facing membrane 14 areconstructed as bevel surfaces 36 with a continuously varying curvaturepassing from the carrier plate surface 12 in the central area of carrierplate 20 into the edge area thereof and without any clearly definedbending lines. The passage into the edge area of carrier plate 20 takesplace following a weld overflow slot 32 in the vicinity of a connectingpoint 38 of membrane 14 to the sealing edge. The bevel surface 36ensures that it is possible to use relatively thick and inflexiblemembrane 14 without any predetermined bending lines and without anyinadmissible material stresses in the membrane fixing area close to theedge. FIGS. 13 and 14 also show that the bevel surface 36 has a planarcentral area in the centre of the transition between carrier platesurface 12 and edge area 16.

In the embodiment of FIGS. 15 to 17, the surfaces of carrier plate 20facing membranes 14 are in each case provided with a plurality ofspacers 39, a system of coolant ducts 41 being formed in carrier platesurface 12 and bevel surface 36. This makes it possible to continuouslysupply with coolant a membrane chamber 48 formed between carrier plate20 and membrane 14, i.e. for example also in the filtration phase shownin FIG. 16, in which the membranes 14 are pressed against carrier plate20 under the pressure of the medium to be filtered. This coolantcontinuously flows through membrane chamber 48 and/or the coolant ductsystem 41, thereby ensuring an effective thermal separation between thecarrier plate 20 and membranes 14. As is clearly shown in FIGS. 15 to17, the spacers 39 are chamfered in the vicinity of bevel surface 36 inorder to obtain a continuous bending of membrane 14 in the variousoperating states.

FIGS. 18 to 20 show a cutout from a filter press, in which the membranefilter plate 10 is in each case arranged between two chamber filterplates 43, which are not provided with membranes. This arrangement fullyutilizes the bulging action of membrane 14, clearly shown in FIG. 20,under the influence of the pressurized flow medium supplied to membranechamber 48 and which simultaneously serves as a coolant in thefiltration phase shown in FIG. 19. In operation, the procedure is suchthat in the filtration phase of FIG. 19, the flow medium is introducedinto membrane chamber 48 under a much lower pressure and/or flowsthrough the coolant channel system 41 with a much lower pressure than inthe pressing phase of FIG. 20.

The aforementioned cooling ducts 41 can naturally also be used in theaforementioned manner as heating medium ducts (FIGS. 15 to 17). It isthen possible to continuously supply membrane chamber 48 with a heatingmedium, which continuously flows through membrane 48 and/or duct system41, so that the temperature of both the carrier plate 20 and moreparticularly the elastic membrane 14 is raised to a higher level thanthat at which the medium to be filtered can be kept.

The features disclosed in the description, drawings and claims can beessential alone, or in random combinations for realizing the variousembodiments of the invention.

We claim:
 1. In a membrane filter plate for a filter press comprising acarrier plate, which includes a central recessed surface in an outersurface, both the outer surface and the central recessed surface beingparallel to a central plane of the carrier plate, a membrane carried onthe outer surface of the carrier plate and a sealing frame including aperiphery, said frame surrounding the carrier plate and the membrane andconnecting the carrier plate and the membrane and sealing the spacebetween the membrane and the central recessed surface against a fluidagent, the improvement comprising said frame comprising a sealing edgebeing spaced from the periphery of said frame and being sealed to themembrane, said sealing edge including a plurality of straight edgeportions interconnected by a plurality of arcuate edge portionscomprising means for providing a corner-less sealing edge sufficient topreclude fatigue of the membrane at these locations.